outlook for mac – drum noise with key press and letters stop appearing on the screen

I am new to mac, but not to outlook.

when I am typing an email, every now and then, a drum noise starts with each key press, and the letters don't appear on the screen.

I have to get the mouse, click at the point in the text where I am typing, and then it works fine. It happens all the time, and only in outlook, not in any other program.

what am I doing wrong?

thank you.